Labeled molecular affinity binding such as immunochromatographic assays have existed for decades and have proven to be an inexpensive way to screen for various conditions such as abused drugs and other conditions such as pregnancy, cancer, or for single or multiple pathogenic conditions such as HIV infection.
In the point-of-care test (POCT) setting, immunochromatographic assays are typical conducted using lateral flow strip technology as described in May et al., U.S. Pat. No. 5,656,503 incorporated herein by reference. Unfortunately, although they can be fast, inexpensive, and simple-to-use, depending on the type of condition being detected, these tests provide a typical accuracy of between 75% and 95%, falling short of the 99% or above accuracy generally considered to be necessary for a confirmatory test, and providing no objective measure of a quantitative result, i.e. the concentration of a given drug present in the liquid being tested.
The reasons for the insufficient accuracy in many rapid IVD test devices are primarily due to their current lack of overall higher sensitivity and specificity. Different samples may contain chemicals or particles which inhibit the rapid and well mixed liquid flow or otherwise interfere with one or both of the first and second affinity binding reactions.
Some devices such as our improved accuracy devices disclosed in our U.S. Pat. No. 8,021,625 (Wang et al.) incorporated herein by reference, may not be sufficiently compact or inexpensive to use in the field.
Other prior devices have attempted to enhance sensitivity or specificity by pretreating various parts of the device with reaction or flow enhancing reagents, pH conditioning chemicals, or even non-specific adhesive blocking molecules which will “block-out” non-analyte molecules which might cause non-specific adhesion, or otherwise compete with the analyte in question for specific binding members, especially in the reaction zones region of the strip. These attempts have met with limited success in some types of testing, but do not provide the desired accuracy in many others. Also, pretreatment with two or more of the above pretreatments exacerbates the difficulties in obtaining uniform manufacturing due to potential incompatibilities between the pretreatment chemicals. For example, the pH conditioner might disrupt the effectiveness of the non-specific blocking member molecules. Or, the manufacturing step of pretreating with the second pretreatment chemical can dislodge some of the first pretreatment chemical.
Further, lot-to-lot variation in the manufacture of many IVD test devices can often lead to ambiguous results, such as false negatives as well as weak false positives, so-called “ghost lines” or “phantom lines”. False negatives typically occur when non-specific molecules interfere with the first and/or second affinity binding actions. It has been found that non-analyte molecules can clump together in liquid samples that are not well mixed so that they temporarily prevent access between analytes and binding members. Even temporary interference in past devices can prevent an adequate number of labeled analyte complexes and/or ultimately immuno-sandwich complexes from forming. In this way, if a non-analyte molecule or clump of molecules blocks access between analytes and binding members for only a few seconds, it may be enough to induce a false negative result. Further, clumps of non-analyte molecules can carry an overabundance of the labeled mobilizable binding members to the second affinity binding site to generate a false positive result.
One area of recent improvement in rapid diagnostic testing involves using the capabilities offered by mobile communication devices such as smart phones. As disclosed in Ozcan et al., U.S. Pat. No. 8,916,390, incorporated herein by reference, a lateral flow-type strip can be automatedly scanned by the camera of a smart phone which can be interpreted by software to obtain a result and deliver it to a wireless network. Lateral flow devices are useful due to their low cost and ease of use. However, prior lateral flow devices suffer from low accuracy as detailed above. This is especially true for saliva testing because of the low concentrations of analytes present. Current lateral flow strips cannot provide the necessary sensitivity and specificity within the time normally allotted to a typical law enforcement action such as a traffic stop.
The low accuracy can be due to a number of problems unique to lateral flow-type tests. First, there is often uneven movement of the immunoparticles within the nitrocellulose membrane. Smaller, non-analyte molecules mixed together with the larger analyte molecules and compete for sites and often prevent the larger molecules from reacting in the desired fashion.
Therefore, there is a need to improve the accuracy of rapid IVD test devices so that rapid inexpensive easily conducted quantitative immunological testing becomes a reality.